1. Field of the Invention
The present invention relates to a moving picture compressed signal changeover apparatus for changing over and outputting plural input digital moving picture compressed signals.
2. Description of the Prior Art
In changeover of transmission video signals or video editing at a broadcasting station, a moving picture changeover apparatus is used. Video signals used at the present are generally analog signals, and output signals are changed over in a boundary of a frame or a field.
When digital signals are used as video signals, compressing and coding is effected to decrease the data quantity.
Methods of compressing and coding a moving picture are described below. The methods of compressing and coding a frame are roughly divided into two types. One is intra-frame coding without utilizing the correlation with other frames, in which the frame can be decoded only from the signal generated by compressing the same frame. The other is inter-frame predictive coding by making use of the correlation with other frames, in which the other frames used in coding must be used in decoding. Inter-frame predictive coding comprises forward predictive coding for making use of the correlation with a preceding picture, backward predictive coding for making use of correlation with succeeding picture, and bidirectional predictive coding for making use of both preceding and succeeding pictures. In a further different coding method, for example, a frame is divided into plural blocks, each block Is differently coded, and these blocks are combined.
In a case of output by changing over the compressed and coded moving picture, If a moving picture signal Is compressed only by intra-frame compressing and coding, by changing over in the boundary of frames, a normal moving picture is output as a reproduced picture even at the changeover point.
However, when changing over and outputting a moving picture slgnal compressed by utilizing the inter-frame correlation, the frame utilizing the correlation at the time of coding and the frame used in decoding may be different before and after the changeover point, so that a moving picture signal not reproduced normally at the changeover point is output.